Process for separation of monotertiary-butylated cresols



United States Patent Ofifice 3,341,657 Patented Sept. 12, 1967 3,341,607PROCESS FOR SEPARATION OF MONO- TERTlARY-BUTYLATED CRESOLS Gerd Leston,Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation ofDelaware Filed Dec. 16, 1965, Ser. No. 514,352 Claims. (Cl. 260-624)This invention relates to a novel complex, the crystal ofmono-t-butylcresol-para-dioxane, and its use in the separation ofisomers from mixtures containing Z-t-butyl- 5-methylphenol and2-t-butyl-4-methylphenol.

A White crystalline complex has been found to be formed fromZ-t-butyI-S-methylphenol and 1,4-dioxane. The complex, having a meltingpoint of 84 0, consists of two molecules of 2-t-butyl5-methylpheno1,

CH3 CH and one mole of 1,4-dioxane.

A crystalline complex also has been found to be formed from2-t-butyl-4-methylphenol and 1,4-di0xane, consisting of nine moleculesof 2-t-butyl-4-methylp-henol (J-CH C a i CH3 and one mole of1,4-dioxane.

The foregoing novel compositions find utility, for example, in theseparation of Z-t-butyI-S-methylphenol from mixtures of2-t-butyl-4-methylphenol and 2-t-butyl-5- methylphenol.

The mixture of meta-, and para-cresol isomers obtained from coal tarusually contains about 60* percent meta-, and 40 percent para-cresol.Due to the close boiling point of these isomers the mixture is soldcommercially instead of the separate isomers.

The butylation of the mixture of meta-, and para-cresol with isobutyleneunder conditions favoring mono-tertiarybutylation results in a mixtureof monobutyl cresols with some dibutyl cresols and isobutylene polymersbeing produced. The separation of the monobutylated products(2-t-butyl-5-methylphenol and 2-t-butyl-4-methylphenol) is not practicalby commercial distillation. Furthermore, a eutectic of the twomonobutylated cresols arises at about the 2:1 ratio(Z-t-butyl-S-methylphenol to 2-t-butyl-4- methylphenol) which would beobtained from a commercial meta-, para-cresol mixture, and precludesseparation of these compounds by crystallization.

I have found that surprisingly 2-t-butyl-4-methylphenol can be readilyseparated from a mixture of 2-t-butyl-5- methylphenol and2-t-butyl-4-methylphenol by the addition of 1,4-dioxane to said mixture.

Upon addition of 1,4-dioxane to a mixture of Z-t-butyl- S-methylphenoland 2-t-butyl-4-methylphenol, a solid complex is formed whichprecipitates from the mixture and may be readily separated therefrom.The solid which is formed comprises a complex formed from two moles of2-t-butyl-5-methylphenol and one mole of 1,4-dioxane. A small amount ofa complex of 2-t-butyl-4-methylphenol and 1,4-dioxane is also formed ina ratio of nine moles of 2-t-butyl-4-methylphenol and one mole of1,4-dioxane.

2 Surprisingly, this fact does not interfere in the upgrading of2-t-butyl- -methylphenol from the crude mixture of the two monobutylatedcresol isomers.

The solid complex which is for-med from two moles ofZ-t-butyI-S-methylphenol and one mole of 1,4-dioxane is readilydecomposed by steam distillation into the separate compounds to yield anazeotrope of 1,4-dioxane and water as overhead while the2-t-butyl-5-methylphenol remains as residue. The2-t-butyl-5-methylphenol thus separated can then be debutylated toobtain pure meta-cresol.

The addition of the 1,4-dioxane to the mixture of2-tbutyl-S-methylphenol and 2-t-butyl-4-methylphenol is preferablycarried out at or slightly above room temperature. The complex formedfrom 2-t-butyl-5-methylphenol and 1,4-dioxane has a melting point of8384 C., and in this process temperatures approaching this melting pointmay be used with the solid complex being formed and precipitating out.Upon cooling of the mixture, further amounts of the solid complexcrystallize as a white crystalline solid. As is known in the art,precipitation may be aided by seeding the mixture with a crystal ofpreviously prepared complex or other known means.

The presence of a hydrocarbon diluent does not affect the reactionbetween 2-t-butyl-5-methylphenol and 1,4- dioxane in the formation of asolid complex and, in fact, be helpful. Suitable diluents would comprisethe aliphatic and alicyclic hydrocarbons having up to eight carbonatoms. These diluents do not sufliciently dissolve the solid complex soas to interfere with its separation but do prevent total solidificationof the mixture and prevent problems which could arise in attempting toseparate the undiluted viscous unreacted constituents from the solidmaterial.

The crystals of 2-t-butyl 5-methylphenol and 1,4-dioxane complex may berecovered by filtering, decanting or other means. The mother liquorremaining is enriched in 2-t-butyl-4-methylphenol and may be used as asource of that compound. It is surprising to note that although2-t-butyl-4-methylphenol also appears to form a complex with dioxane,the complex being formed in a ratio of nine moles of2-tbutyl-4-methylphenol to one mole of 1,4-d1oxane, this formation doesnot interfere with the butyl-S-methylphenol from a mixture butylatedcresols. Also, 1,4-dioxane was not found to form a solid complex whenadmixed with similar phenolic compounds such as meta-cresol,meta-isopropylphenol, 2,4-xylenol, or p-isopropylphenol.

The process of this invention is schematically illustrated in theaccompanying drawing by flow diagram.

The invention is further illustrated in the following examples.

EXAMPLE I To a beaker containing 1,4-dioxane there was addedZ-t-butyl-S-methylphenol. A slight temperature rise was noted and asolid precipitated. The solid was separated and twice recrystallizedfrom hexane to yield crystals having a melting point of 83-84 C.Infrared analysis of these crystals was made using a mineral oil mull.The crystals exhibited identical absorption characteristic of bondedphenolic OH, Z-t-butyI-S-methylphenol structure, and 1,4-di0xanestructure consistent with a structure for a 2- t-butyl-S-methylphenoland 1,4-dioxane complex. Quantitatively, the crystals were analyzed byinfrared in chloroform solution and were found to contain 67.5:1 molepercent Z-t-butyl-S-methylphenol and 32.5:1 mole percent l,4-dioxane,characteristic of a complex comprising two moles ofZ-t-hutyl-S-methylphenol and one mole of 1,4-dioxane.

' 3 EXAMPLE 11 EXAMPLE III A mixture of 2-t butyl-5-methylphenol and2-t-butyl- 4-methylphenol, prepared from the monobutylation of acommercial meta-, para-cresol mixture was analyzed and found to be 63.4percent 2-t-butyl-5-methylphenol, 35.2 percent 2-t-butyl-4 methylphenoland 1.4 percent impurities such as isobutylene low molecular weightpolymers, residual cresols, etc. To 20 grams of this mixture(corresponding to 12.78 grams, 0.08 mole, of 2-t-butyl5-methylphenol)was added at room'temperature 3.40 grams (0.04 mole) of 1,4-dioxane.Upon dissolution of the 1,4- dioxane in the noted. The mixture wasseeded with previously prepared complex of Z-t-butyl-S-methylphenol and1,4-dioxane. The mixture warmed and a solid precipitated to form aslurry. The slurry was cooled to room temperature and filtered to give11.5 grams of a white solid melting at 7482.-5 C. The filtrate, 10.4grams, together with the solid amounted to a total of 21.9 grams of 94percent recovery of the starting materials. Ten

grams of the crude solid complex was recrystallized from hexane. Atotalof 9.7 grams of complex was 20 ml. of recovered from therecrystallization.

The recrystallized complex melted at 82.585 C. Vapor phasechromatographic analysis of the 11.50 grams of solid showed it tocontain 2.59 grams of 1,4-dioxane, 8.33 grams ofZ-t-butyI-S-methylphenol and only a minor amount (0.58 gram) of2-t-butyl-4-methylphenol. The 2-tbutyl-S-methylphenol recovered amountedto 66 percent of that present in the original mixture.

EXAMPLE IV EXAMPLE v A 49.5 gram sample of solid complex produced inExample 111 (78.85 percent ,Z-t-butyl-S-methylphenol and 21.15 percent1,4-dioxane) and 200 milliliters of distilled water were placed in aflask. Using a one foot glass helix packed column, this mixture wasdistilled at atmospheric pressure. The initial boiling point of thedistillate was 87 C. but was difiicult to maintain at this lowertemperature except at very high reflux ratio. The temperature of thedistillate slowly rose to 100 C. as 12.0 milli liters, 12.3 grams wasanalyzed by vapor phase chromatograph analysis and showed 72.5 percent1,4-dioxane which corresponds to 8.92 grams or 85 percent of a dioxanein the solid complex starting ma- 7 percent dioxane and 3.75

terial. Therewas no 2-t-butyl-5-methylphenol found in the distillate.The residue in the distillation flask consisted of tWo layers, an oilyupper layer and a lower aqueous layer. The oily layer was separated andweighed to give 36.8 grams of material which was analyzed and found tobe 96.0 percent Z-t-butyl-S-methylphenol. The impurities in the2-t-butyl-5-methylphenol oily layer comprised 0.25 percent water. Thisrecovery amounts to 90 percent of the Z-t-butyl-S-methylphenol in thecomplex starting material.

EXAMPLE VI To a 3-neck, 500 milliliter flask equipped with a droppingfunnel, mechanical stirrer, thermometer and re-.

flux condenser there was charged 52.0 grams of complex ofZ-t-butyl-S-methylphenol and 1,4-di0xane.(corresponding to 41 grams of2-t-butyl-5-methylphenol). To this was added 32 milliliters of methanoland 10.5 grams of concentrated hydrochloric acid. To this was added 9.9grams n-butyraldehyde (0.14 mole) at a dropwise rate over a 45 minuteperiod at a temperature of 3540 C. The mixture was refluxed (8277 C.)for a period of three hours. It was then transferred to a 600 milliliterbeaker and 250 milliliters of water and 250 milliliters of n-hexane wereadded. On cooling,

a solid precipitated which was filtered.

The solid weighed 33.7 grams. The solid melted at 207-2108 C. andcorresponds to a 70.6 percent yield of,

4,4'-butylidenebis(2-t-butyl-5-methylphenol) based on theZ-t-butyl-S-methylphenol present in ing material. The melting point of4,4'-butylidene bis (2-tbutyl-S-methylphenol) reported by D. 1. Beaveret al., Journal of the Amer. Chem. Soc., 74, p. 3410 (1952) is 210-210.7C. a

I claim: 1. The complex consisting of two molecules of2-tbutyl-S-methylphenol and one molecule of 1,4-dioxane. 2. The complexconsisting of nine molecules of 2-tbutyl-4-methylphenol and one moleculeof 1,4-dioxane. 3. Process for separating 2-t-butyl-S-methylphenol froma mixture of Z-t-butyl-S-methylphenol and 2-t-butyl- 4-methylphenolcomprising:

adding 1,4-dioxane to said mixture to form a solid com-' plex comprisedmainly of 2-t-butyl-i5-rnethylphenol and 1,4-dioxane, separating saidsolid complex from said mixture, decomposing said solid complexto give2-t-butyl-5- methylphenol. and 1,4-dioxane, and recovering substantially;pure Z-t-butyI-S-methylphenol therefrom. 4. The process of claim 3 inwhich said complex is de composed by distilling said complex in thepresence of water. a V

5. The process of claim 3 wherein a hydrocarbon solvent selected fromthe group consisting of aliphatic and alicyclic hydrocarbons having upto eight carbon atoms is present with said mixture of2-t-butyl-4-methylphenol and 2-t-butyl-5-methylphenol.

References Cited UNITED STATESPATENTS 2,863,927 12/1958 Parisse 260--624LEON ZITVER, Primary Examiner. H. ROBERTS, Assistqnt Examiner,

the complex start-

3. PROCESS FOR SEPARATING 2-T-BUTYL-5-METHYLPHENOL FROM A MIXTURE OF2-T-BUTYL-5-METHYLPHENOL AND 2-T-BUTYL4-METHYLPHENOL COMPRISING: ADDING1,4-DIOXANE TO SAID MIXTURE TO FORM A SOLID COMPLEX COMPRISED MAINLY OF2-T-BUTYL-5METHYLPHENOL AND 1,4-DIOXANE, SEPARATING SAID SOLID COMPLEXFROM SAID MIXTURE, DECOMPOSING SAID SOLID COMPLEX TO GIVE2-T-BUTYL-5METHYLPHENOL AND 1,4-DIOXANE, AND RECOVERING SUBSTANTIALLYPURE 2-T-BUTYL-5-METHYLPHENOL THEREFROM.